The present invention relates generally to fluid dispensing; but more specifically, though not exclusively, to the dispensing of multiple-part components such as highly viscous epoxies, urethanes, silicones, plastic adhesives and other similar fluid materials to be used, for example, as gasket sealing beads, or for the injection-filling of grooves or closed cavities and the like, particularly where visual inspection of the degree of cavity filling is not possible and a guarantee of complete cavity filling is desired.
The successful dispensing of such fluid materials has heretofore been achieved with, for example, disposable, pre-loaded dual fluid/component cartridges adapted to be attached and removed from dispensing apparatus that, under hydraulic or pneumatic pressure, or preferably electric motor control, forces the fluid components into a mixer and then through a dispensing nozzle or opening to the ultimate receptacle or work-piece, such as is described in my earlier U.S. Pat. Nos. 5,816,445; 6,050,450; 6,089,407 and PCT/IB99/02052.
There are special applications, however, where an improved degree of control and monitoring may be required, as in the before-mentioned application to closed or hidden cavities and the like where uniform, constant and complete filling of the cavity is essential but visual inspection is not possible; or where uniform and constant cross-section sealant or other gasket beads or the like are to be laid down, as in grooves or otherwise.
It is to the assuring or guaranteeing of such results, that the present invention is primarily directed, calling for significant improvement in the ability to inject such fluid material into a closed cavity to a defined pressure; and, additionally, to a novel capability to create constant flow rate through fluid coupling or delivery flexible hoses, particularly where the dispensing head is some distance from the fluid pumps or other force-applying mechanisms.
As disclosed in the above-cited exemplary patents, electric motor power is often preferred for controlling the developing of the fluid-dispensing injection forces; and, in accordance with the present invention, the preferred fluid dispensing apparatus is under the control of later-described electrically controlled gear pumps.
In summary, however, from one of its important aspects, the invention embraces a method of dispensing viscous fluids that when mixed are to fill a cavity, that comprises, injecting the fluids from a source under pressure along a resiliently flexible volume-expandable conduit connected to a common mixing dispenser; dispensing the fluids from the mixing dispenser into the inlet of a cavity-to-be-filled thereby; adjusting the pressure of the fluid injection to a predetermined value normally required completely to fill the cavity; increasing the pressure further above said predetermined value to guarantee such complete cavity filling, with the conduit flexibly expanding to accommodate for the increased pressure; thereupon shutting off the cavity inlet from the conduit; enabling the fluid from the expanded conduit to flow back to the source to relieve pressure if desired; and disconnecting the dispenser from the cavity inlet.
A most commonly used mixing element in metered mix systems is the static mixer, which has the advantage that it mixes material without injecting air. Static mixers, however, present a considerable resistance to flow and this resistance is not linear. Twice the flow rate, for example, will actually produce more than twice the resistance to flow. The higher the viscosity of the fluid material, moreover, the higher the flow resistance. Combinations of high viscosity and speed can even require pressures in excess of 1000 PSI (pounds per square inch).
As above pointed out, the flow rate effect particularly becomes a problem in systems where the dispensing head is remote from the pumpsxe2x80x94a configuration that exists in many, if not a majority of dispensing systems. The uneven flow is especially problematic in a typical situation where the user is trying to lay down a constant cross-section bead. An example of this would be a gasket bead application where the dispensing head is attached to an end effector on a XYZ positioning table. In these cases, it is not unusual for the pumps to be connected to the dispensing head by several feet of flexible hose. When dispensing of the bead first starts, the flow rate is slower, and therefore the cross-section of the bead is smaller than specified. This is because the flow resistance of the static mixer causes the hose to expand until the pressure drop across the static mixer equals the pressure inside the hose. During this time, part of the material will go into expanding the hose and a part will go through the static mixer. The resulting cross section of the bead consequently will deleteriously vary until the pressure is in equilibrium.
This problem is solved, in accordance with a feature of the present invention, by a novel combined use with the flexible hose of a pressure sensor, an integral shut-off valve and a novel microprocessor control and software, all as later more fully explained. The user first determines the required pressure to dispense the bead. Previously, when the system first starts up, it feeds material through the static mixer so that the static mixer is full. When the fluid pumps start, the integral shut-off valve is kept closed until the pressure inside the hose reaches the required dispensing pressure. At such time, two events happen simultaneously: (1) a signal is sent to the XYZ table to begin dispensing the bead; and (2) the integral shut-off valve is opened to begin the flow. Since the required pressure was built up before the start of the dispensing, however, when the dispensing starts, all the pumped material flows through the static mixer, providing for a constant flow rate. This constant flow rate now creates the sought-after bead with a constant cross-section.
The second problem of uniform and complete cavity filling is also solved by the combined use of the above-mentioned features, enabling also the ability to fill a closed cavity to a predefined pressure. An example of this is when, as an illustration, only 100 PSI pressure is required to fill a closed cavity and, yet 500 PSI is required to assure that the smallest recess of the cavity has been totally filled. To perform this function, a seal is first established between the outlet of the static mixer and the cavity to be filled. Dispensing is started and continues until the cavity is filled. During this phase, the pressure sensors read 100 PSI. But once the cavity is filled, the material can only go into the flexible hose, expanding it, and the resulting pressure will increase. This pressure will also be transmitted to the cavity, insuring its total filling. Once the 500 PSI pressure is reached, the integral shut-off valve is activated and the dispensing is terminated.
For two-component dispensing, a pair of the before-mentioned gear pumps can be geared together to turn at a fixed ratio as later more fully explained; or they can be driven individually, in which case it becomes a variable ratio system. Driving the pumps individually allows them to pump at different speeds from each other. If, for example, one pump turns twice as fast as the other pump, the dispensing ratio will be 2:1, etc. When dispensing two-part materials, moreover, the volume ratio is programmable, as is the speed of dispensing. Preferably, also as later fully described, all motors operate closed loop, with each having an encoder attached to its shaft. The encoder sends a feedback signal to the microprocessor such that the verification of the gear pumps speed is in real-time.
Preferred embodiments and best mode designs are later presented.